There is presently a wide market for video tape recorders which are constructed to be connected to home television receivers, and which may be set automatically to record selected television programs.
The principal objective of the present invention is to provide a simple and inexpensive unit which may be connected to such a video tape recorder and which responds to the television signals being recorded thereby to interrupt the recording process for the duration of each commercial so as to enable the television program to be recorded free of commercials.
During a television broadcast, when the program changes to a commercial, both the video and audio components of the composite television signal to fade to a low amplitude level. This momentary loss of both the video and audio signal components at the beginning of each commercial is used in the system of the invention to cause the remote pause control of the video tape recorder to interrupt the recording process for a selected interval, corresponding to the length of the commercial.
The pause interval may be selected by generating a missing signal pulse each time there is a loss in both the video and audio signal components, and by applying the missing signal pulses to a one-shot, or equivalent circuit, that has been set to time out, for example, in a few seconds after thirty seconds, or at the end of some other selected time interval, depending upon the length of the individual commercials usually encountered in the program being recorded.
In one operational mode of the unit, a missing signal pulse is generated during the transition between the program and a commercial. This pulse will trigger the one-shot and cause the video tape recorder to interrupt its recording process for thirty-two seconds, that is, until the one-shot times out. If a second commercial is received immediately after the first commercial, a second missing signal pulse will be generated before the one-shot has had a chance to time out and will trigger the one-shot to an additional thirty-two seconds. Accordingly, the one-shot will remain in its triggered state for so long as a succession of thirty-second commercials are being received. A limitation in the operation of the unit in this mode is that it will also respond to a missing signal pulse generated during the transition between the last commercial of the group and the resumption of the program, so that thirty-two seconds of the initial portion of the resumed program will be lost. Usually the loss of information is sufficiently slight so as not to be noticeable to the viewer.
In a second operational mode, the unit responds to the first missing signal pulse generated during the transition between the program and the first commercial to put the video tape recorder in "Pause" for two minutes. This time corresponds to the time interval usually allotted to each group of commercials during commercial television broadcasting. During this latter operational mode, the unit will time out at the end of two minutes so that, normally, there will be no loss of program, as occurs when the unit is in its first operational mode, as explained in the previous paragraph.
The embodiment to be described has a feature, in that it will be maintained in its two-minute mode, only so long as missing signal pulses are received every thirty seconds to indicate that a group of successive commercials are being received during the two-minute interval. If such a missing signal pulse is not received, the unit will time out at the end of the following thirty-two seconds and the recording process will be resumed.